I’ve really enjoyed Olivia Judson’s columns on Times $elect. They’ve been funny, eloquent and haven’t shied away from the biological nitty-gritty. In her last column, she ends with a meditation on three questions she wants evolutionary biologists to solve:
The first is metamorphosis. Everyone knows a caterpillar becomes a butterfly; and it is easy to work out why it might be useful to split your life between growing (caterpillar) and loving (butterfly). But what I find peculiar is the manner of becoming a butterfly: within the pupa, the caterpillar breaks down its body, including much of its brain, and reconstitutes itself along different lines. It’s a kind of reincarnation. I’d love to know how this evolved. (This may already be known to someone; if it is, I have so far failed to discover to whom.) Even weirder are some of the transformations that take place in the sea. Here, animals such as sea urchins actually change the symmetry of their bodies when they metamorphose — they go from bilateral symmetry, like a human face, to radial symmetry, like a wheel. Weirder still, rather than recycle their old bodies, as caterpillars do, many of the marine critters throw large chunks of their old bodies away. The evolution of such radical transformations seems hard to imagine — and yet, it’s a phenomenon that has arisen many times, so it can’t be that hard to evolve.
The second is meiosis. This is the kind of cell division by which sperm and eggs are made — so it’s essential for sex as we know it. Meiosis is a strange — and horrendously involved — procedure. Why strange? Well, each of us has two sets of chromosomes — one from our mother, and one from our father. When we make eggs or sperm, we divide up our two sets so that each egg or sperm has one complete set. You might think that to do this, you’d just divide the precursor cell in two, with each descendant having one set of chromosomes. But no. You double the chromosomes — four sets — then split the cell into two, then two again. Odd. But it’s how meiosis could have evolved that really makes my mind boggle. Here, working out the early steps is complicated by the fact that meiosis seems to have evolved only once — most organisms seem to be doing minor variations on the same major theme — so we can’t compare and contrast. Worse, the origins of meiosis are shrouded in the mists of deep time.
Speaking of deep time brings me to my third puzzling phenomenon: the origin of life. This, of course, is the biggest mystery in all biology. Did life arise here, or arrive here? If it arose here, how? We can at least imagine the basic steps. One of the first is the invention of membranes — for living cells are separate compartments, and membranes are the containers. Or, if life arrived here, where did it come from — and where did it start? Are other planets home to life — and if so, what are they like?